Two-stage optical switch circuit network

ABSTRACT

An optical switch circuit network includes r input optical switches  102   a  each having n input ports, m 1×r optical switches  125   a , and an n×m optical switch for switching a path connecting the input ports and the 1×r optical switches, and r output optical switches  125  each having r×1 optical switches, n output ports, and an m×n optical switch for switching a path connecting the output ports and 1×r optical switches. The i-th 1×r optical switch of each input optical switch is connected to the i-th r×1 optical switch of each output optical switch.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical switch circuit network forcontrolling paths for the propagation of optical signals.

2. Description of the Background Art

It has been customary to implement a number of input ports and outputports, i.e., a large-scale architecture with optical switches bysequentially combining the optical switches. Various schemes heretoforeproposed for combining optical switches include an optical pathcross-connect system taught in T. Nishi, et al. “Optical SwitchArchitectures for Optical Path Cross-Connect”, Proceedings of the 1998General Conference of the Institute of Electronics, Information andCommunication Engineers of Japan, B-10-97, March 1998. The cross-connectsystem constitutes an optical switch circuit network with optical matrixswitches arranged in three consecutive stages. This, however, bringsabout a substantial loss in the optical matrix switches. Effectivearchitectures for increasing the number of input ports and output portswith two stages of optical matrix switches have not been reported yet.

An optical switch circuit network using thermo-optical (TO) switches isdisclosed in A. Watanabe, etal. “8×16 delivery and coupling switch boardfor 320 Gbit/s throughput optical path cross-connect system”,Electronics Letters, Vol. 33, No. 1, pp. 67-68, Jan. 2, 1997. The TOswitches each include means for switching an optical path by varying theresistance of an optical waveguide with heat. Each TO switch is locatedat the intersection of one input and one output. The network drives onlyone of the TO switches connected to a desired input and a desired outputfor the purpose of saving drive power.

However, the problem with the above TO switch scheme is that it has toserially connect TO switches equal in number to the inputs or theoutputs and therefore results in a prohibitive total length.Specifically, when the TO switch scheme is used to construct an N×Noptical switch circuit network, it is necessary to switch Nlog₂N TOswitches at the input port side and switch Nlog₂N TO switches at theoutput port side. In the worst case, therefore, the network has toswitch 2Nlog₂N TO switches in total.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an opticalswitch circuit network needing only two stages of optical matrixswitches.

It is another object of the present invention to provide an opticalswitch circuit network capable of scaling down the individual opticalmatrix switch.

It is a further object of the present invention to provide an opticalswitch circuit network which is short despite the use of TO switches andcapable of reducing power necessary for driving TO switches whilestabilizing the power.

In accordance with the present invention, an optical switch circuitnetwork including nr (n and r being positive integers) input ports andnr output ports includes r input optical switches arranged at the inputside and each having n of the nr input ports, m (m being a positiveinteger) 1×r optical switches and an n×m optical switch for selectivelyconnecting the n input ports and m 1×r optical switches, and r outputoptical switches arranged at the output side and each having n of the nroutput ports, m r×1 optical switches and an m×n optical switch forselectively connecting said n output ports and m r×1 optical switches.The i-th (i being an integer between 1 and m) 1×r optical switch of eachof the input optical switches is connected to the i-th r×1 opticalswitch of each of the output optical switches.

Also, in accordance with the present invention, an optical switchcircuit network including nr input ports and nr output ports includesr/h (h being a positive integer) input optical switches arranged at theinput side and having nh of the nr input ports, m h×r optical switchesand h n×m optical switches each being connected to a particular one of nof the nr input ports to thereby switch a path between the n input portsand said m h×r optical switches, and r/h optical output switchesarranged at the output side and having nh of the nr output ports, m r×hoptical switches and h m×n optical switches each being connected toparticular one of n of the nr output ports to thereby switch a pathbetween the n output ports and the m r×h optical switches. The i-th (ibeing an integer between 1 and m) h×r optical switch of each of theinput optical switches is connected to the i-th r×h optical switch ofeach of the output optical switches by a tape-like optical fiberconstituted by h connect lines.

Further, an optical switch circuit network including nr input ports andnr output ports of the present invention includes r/h input opticalswitches arranged at the input side and having nh of the nr input ports,m/h′ (h′ being a positive integer) nh×h′r optical switches and nh/h′h′×m/h′ optical switches each being connected to particular one of h′ ofthe nr input ports to thereby switch a path between the h′ input portsand m/h′ nh×h′r optical switches, and r/h output optical switchesarranged at the output side and having nh of the nr output ports, m/h′h′r×nh optical switches and nh/h′ m/h′×h′ optical switches each beingconnected to particular one of h′ of the nr output ports to therebyswitch a path between the h′ output ports and h′r×nh optical switches.The h′×m/h′ optical switches each are connected to said nh×h′ opticalswitches by tape-like optical fibers each comprising h′ connect lines.The m/h′ optical switches each are connected to the r/nh opticalswitches by tape-like optical fibers each having h′ connect lines. Theinput optical switches are connected to the output optical switches bytape-like optical fibers each having h connect lines.

Moreover, in accordance with the present invention, an optical switchcircuit network including N input ports and N output ports includes2^(n) input sections each having N/2^(n) of the N input ports, 2^(n)N/2^(n)×N/2^(n) input optical switches, and 1×2 optical switchesarranged in an n-stage tree configuration and connecting the input portsand input optical switches, and 2^(n) output sections each havingN/2^(n) of the N output ports, 2^(n) N/2^(n)×N/2^(n) output opticalswitches, and 1×2 optical switches arranged in an n-stage treeconfiguration and connecting the output ports and output opticalswitches. The j-th (j being an integer between 1 and 2^(n)) inputoptical switch of the i-th (i being an integer of 2^(n) or smaller)input section is connected to the i-th output optical switch of the j-thoutput section.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention will become moreapparent from the consideration of the following detailed descriptiontaken in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram schematically showing the general constructionof an optical switch circuit network in which optical matrix switchesare arranged in three consecutive stages;

FIG. 2 is a schematic block diagram showing an optical switch circuitnetwork embodying the present invention;

FIG. 3 is a schematic block diagram useful for understanding theconfiguration of an optical matrix switch included in the network ofFIG. 2;

FIG. 4 is a schematic block diagram showing the optical matrix switchincluded in the network of FIG. 2;

FIG. 5 is a schematic block diagram showing an alternative embodiment ofthe present invention;

FIG. 6 is a schematic block diagram for describing the configuration ofan optical matrix switch included in the network of FIG. 5;

FIG. 7 is a schematic block diagram showing the optical matrix switchincluded in the network of FIG. 5;

FIG. 8 is a schematic block diagram showing another alternativeembodiment of the present invention;

FIG. 9 is a schematic block diagram showing still another alternativeembodiment of the present invention;

FIGS. 10-12 are schematic block diagrams each showing a specificconfiguration of an optical device included in the embodiment of FIG. 9;and

FIGS. 13-17 are schematic block diagrams each showing a further anotheralternative embodiment of the present invention.

In the drawings, identical reference numerals designate like structuralelements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

To better understand the present invention, brief reference will be madeto the general construction of an optical switch circuit network havinga three-stage cross-connect configuration, shown in FIG. 1. As shown,the switch circuit network, generally 50, includes optical matrixswitches 52 a-1 through 52 a-r arranged at the first stage, opticalmatrix switches 52 b-1 through 52 b-m arranged at the second stage, andoptical matrix switches 52 c-1 through 52 c-r arranged at the thirdstage. The suffixes r and m are representative of positive integers.

In the specific network of FIG. 1, n input ports are connected to eachof the matrix switches 52 a-1 through 52 a-r constituting the firststage. Likewise, n output ports are connected to each of the matrixswitches 52 c-1 through 52 c-r constituting the thirdstage. The entirenetwork 50 therefore has nr inputs and nr outputs, i.e., an nr×nrconfiguration.

The matrix switch 52 a-1 included in the first stage is connected to allof the matrix switches 52 b-1 through 52 b-m of the second stage.Likewise, the other matrix switches 52 a-2 through 52 a-r of the firststage each are connected to all of the matrix switches 52 b-1 through 52b-m of the second stage. Therefore, the matrix switches 52 a-1 through52 a-r each have n inputs and m outputs, i.e., an n×m configuration.

The matrix switch 52 b-1 included in the second stage is connected toall of the matrix switches 52 c-1 through 52 c-r of the third stage.Also, the other matrix switches 52 b-2 through 52 b-m of the secondstage each are connected to all of the matrix switches 52 c-1 through 52c-r of the third stage. Therefore, the matrix switches 52 b-1 through 52b-m each have r inputs and r outputs, i.e., an r×r configuration. Thematrix switches 52 c-1 through 52 c-r each have m inputs and n outputs,i.e., an m×n configuration.

The entire switch circuit network 50 therefore has nr inputs and nroutputs, as mentioned earlier. If a relation of m≧2^(n)-1 is satisfied,then the network 50 is fully non-blocking, as well known in the art.

Referring to FIG. 2, an optical switch circuit network embodying thepresent invention is generally designated by the reference numeral 100.The illustrative embodiment constitutes an improvement over theconventional optical switch circuit network 50. As shown, the network100 primarily differs from the network 50 in that it has optical matrixswitches arranged only in two stages. Specifically, the network 100 ismade up of optical matrix switches 102 a-1 through 102 a-r and opticalmatrix switches 102 b-1 through 102 b-r arranged at its input side andits output side, respectively.

Briefly, the matrix switches 102 a-1 through 102 a-r at the input sideeach are the combination of a corresponding one of the first-stagematrix switches 52 a-1 through 52 a-r of the conventional network 50 anda corresponding one of the input portions of the second-stage matrixswitches 52 b-1 through 52 b-m. Likewise, the matrix switches 102 b-1through 102 b-r at the output side each are the combination of acorresponding one of the third-stage matrix switches 52 c-1 through 52c-r of the conventional network 50 and a corresponding one of the outputportions of the second-stage matrix switches 52 b-1 through 52 b-m. Thematrix switches 102 a-1 through 102 a-r and matrix switches 102 b-1through 102 b-r are symmetrical in configuration to each other withrespect to inputs and outputs. Let the following description concentrateon the arrangements of the first-stage matrix switches 102 a-1 through102 a-r in order to avoid redundancy.

To constitute the matrix switches 102 a-1 through 102 a-r, assume thatthe second-stage matrix switches 52 b-1 through 52 b-m of theconventional network 50 each are divided into an input portion and anoutput portion at its center, and that the input portions of the matrixswitches 52 b-1 through 52 b-m each are connected to the first-stagematrix switches 52 a-1 through 52 a-r. FIG. 3 shows a specificconfiguration of one of the matrix switches 52 b-1 through 52 b-mbisected at its center M. Because the matrix switches 52 b-1 through 52b-m may have an identical configuration, only the matrix switch 52 b-1will be described by way of example with reference to FIG. 3.

As shown, the matrix switch 52 b-1 includes optical switches 125 a-1through 125 a-r respectively connected to the r inputs and opticalswitches 125 b-1 through 125 b-r respectively connected to the routputs. In the specific configuration of FIG. 3, r is assumed to be 4for the sake of illustration. The optical switches 125 a-1 through 125a-r at the input side each have a single input and r outputs (1×r) whilethe optical switches 125 b-1 through 125 b-r each have r inputs and asingle output (r×1). The optical switches 125 a-1 through 125 a-r eachare cross-connected to all of the optical switches 125 b-1 through 125b-r.

Each of the matrix switches 52 b-1 through 52 b-m includes the aboveoptical switches 125 a-1 through 125 a-r. It follows that the entireswitch circuit network 100 includes m optical switches 125 a-1 through moptical switches 125 a-r. In the following description, the m opticalswitches 125 a-1 included in the input portions of the matrix switches52 b-1 through 52 b-m are considered as a group. Generally, m opticalswitches 125 a-i (i being an integer between 1 and r, inclusive)included in the input sides are considered as a group.

As shown in FIG. 4, the matrix switch 102 a-1, FIG. 2, included in theillustrative embodiment is a device implemented by the combination ofthe above group of m optical switches 125 a-1 and first-stage matrixswitch 52 a-1, FIG. 1. The matrix switch 52 a-1 has n inputs and moutputs, as stated earlier. The n inputs are respectively connected tothe input ports of the network 100 of the illustrative embodiment whilethe m outputs are respectively connected to the m optical switches 125a-1. Generally, the matrix switch 102 a-i (i being an integer between 1and r, inclusive) of the network 100 is a device implemented by thecombination of the group of m optical switches 125 a-i and first-stagematrix switch 52 a-i of the conventional network 50.

The matrix switches 102 b-1 through 102 b-r at the output side areidentical in configuration with the matrix switches 102 a-1 through 102a-r except for the following. The optical switches 125 b-1 through 125b-r of each of the second-stage matrix switches 52 b-1 through 52 b-mare rearranged in the same manner as at the input side and combined withthe third-stage matrix switches 52 c-1 through 52 c-r of theconventional network 50.

The switch circuit network 100 with the above configuration successfullyimplements the same number of input ports and output ports as thethree-stage type network 50 only with two stages of matrix switches.

Reference will be made to FIG. 5 for describing an alternativeembodiment of the present invention. As shown, an optical switch circuitnetwork, generally 200, has optical matrix switches 202 a-1 through 202a-(r/h) at its input side and has optical matrix switches 202 c-1through 202 c-(r/h) at its output side. The suffix h is representativeof r or a smaller positive integer. The network 200 is representative ofa more general configuration of the previous network 100 and identicalwith the network 100 when h is 1.

The matrix switches 202 a-1 through 202 a-(r/h) at the input side eachare the combination of a corresponding one of the first-stage matrixswitches 52 a-1 through 52 a-r of the conventional network 50 and theinput portions of the second-stage matrix switches 52 b-1 through 52b-m. Likewise, each of the matrix switches 202 c-1 through 202 c-(r/h)at the output side is the combination of a corresponding one of thethird-stage matrix switches 52 c-1 through 52 c-r of the conventionalnetwork 50 and the output portions of the second-stage matrix switches52 b-1 through 52 b-m. The matrix switches 202 a-1 through 202 a-(r/h)and matrix switches 202 c-1 through 202 c-(r/h) are symmetrical inconfiguration to each other with respect to inputs and outputs. Let thefollowing description concentrate on the arrangements of the matrixswitches 202 a-1 through 202 a-(r/h) in order to avoid redundancy.

Again, to constitute the matrix switches 202 a-1 through 202 a-(r/h),assume that the second-stage matrix switches 52 b-1 through 52 b-m ofthe conventional network 50 each are divided into an input portion andan output portion at its center, and that the input portion of each ofthe matrix switches 52 b-1 through 52 b-m is connected to thefirst-stage matrix switches 52 a-1 through 52 a-r. FIG. 6 shows aspecific configuration of one of the matrix switches 52 b-1 through 52b-m bisected at its center M. Because the matrix switches 52 b-1 through52 b-m may have an identical configuration, as stated previously, onlythe matrix switch 52 b-1 will be described by way of example withreference to FIG. 6.

As shown, the r×r matrix switch 52 b-1 has r/h groups of h inputs.Optical switches 225 a-1 through 225 a-(r/h) are arranged at the inputside of the matrix switch 52 b-1, and each are connected to a particularone of the r/h input groups. Optical switches 225 b-1 through 225b-(r/h) are arranged at the output side of the matrix switch 52 b-1, andeach is connected to a particular one of r/h output groups. In FIG. 6, his assumed to be 4 for the sake of illustration.

The optical switches 225 a-1 through 225 a-(r/h) at the input side eachhave h inputs and r outputs (h×r) while the optical switches 225 b-1through 225 b-(r/h) each have r inputs and h outputs (r×h). The opticalswitches 225 a-1 through 225 a-(r/h) each are cross-connected to all ofthe optical switches 225 b-1 through 225 b-(r/h) by bundles 801 eachhaving h connect lines. Each bundle 801 of h connect lines may beimplemented by h optical fibers arranged in the form of a tape or strip.

Each of the m matrix switches 52 b-1 through 52 b-m includes the aboveoptical switches 225 a-1 through 225 a-(r/h). It follows that the entireswitch circuit network 200 includes m optical switches 225 a-1 through moptical switches 225 a-r/h. The m optical switches 225 a-1 at the inputside are therefore considered as a group. In general, m optical switches225 a-i (i being an integer between 1 and r, inclusive) at the inputside are considered as a group.

As shown in FIG. 7, the matrix switch 202 a-1, FIG. 5, included in theillustrative embodiment is a device implemented by the combination ofthe above group of m optical switches 225 a-1 and h first-stage matrixswitches 52 a-1. Each matrix switch 52 a-1 has n inputs and m outputs,as stated earlier. The n inputs are respectively connected to n of then×h input ports of the network 200 of the illustrative embodiment whilethe m outputs are respectively connected to the m optical switches 225a-1. In general, the matrix switch 202 a-i (i being an integer between 1and (r/h), inclusive) of the network 200 is a device implemented by thecombination of the group of m optical switches 225 a-i and h first-stagematrix switches 52 a-i of the conventional network 50.

The matrix switches 202 c-1 through 202 c-(r/h) at the output side areidentical in configuration with the matrix switches 202 a-1 through 102a-(r/h) except for the following. The optical switches 225 c-1 through225 c-(r/h) of each of the second-stage matrix switches 52 b-1 through52 b-m are rearranged in the same manner as at the input side andcombined with the third-stage matrix switches 52 c-1 through 52 c-r ofthe conventional network 50.

The switch circuit network 200 with the above configuration is alsosuccessful to implement the same number of input ports and output portsas the three-stage type network 50 only with two stages of matrixswitches.

Another alternative embodiment of the present invention will bedescribed with reference to FIG. 8. As shown, an optical switch circuitnetwork includes matrix switches 302 a-1 through 302 a-r (see FIG. 9)arranged at the input side and which are the improved version of thematrix switches 102 a-1 through 102 a-r of the network 100. Because thematrix switches 302 a-1 through 302 a-r are identical in configuration,the following description will concentrate on the matrix switch 302 a-1shown in FIG. 9. The matrix switches 102 b-1 through 102 b-r at theoutput side each are replaced with improved one symmetrical inconfiguration to the matrix switch 302 a-1.

To implement the matrix switch 302 a-1 of the illustrative embodiment,assume that the configuration shown in FIG. 8 is substituted for thematrix switch 102 a-1 shown in FIG. 4. As shown in FIG. 8, the matrixswitch 102 a-1 includes the matrix switch 52 a-1 having n inputs and moutputs and m optical switches 125 a. The matrix switch 52 a-1 is madeup of n optical switches 351 a arranged at the input side and m opticalswitches 351 b arranged at the output side. Each optical switch 351 aand each optical switch 351 b have a 1×m configuration and an n×1configuration, respectively. The optical switches 351 a each areconnected to all of the optical switches 351 b by connect lines 352.

In the illustrative embodiment, the above connect lines 352 each aredivided into two so as to form a group of n 1×m optical switches 351 aand a group of m n×1 optical switches 351 b. Then, the m n×1 opticalswitches 351 b each are connected to one of them 1×r optical switches125 a following it, thereby newly constituting n×r optical devices 361shown in FIG. 9. The optical devices 361 each control the path for asingle optical signal.

FIGS. 10-12 each show a particular configuration of the above n×roptical device 361. FIG. 10 shows a so-called Banyan network having 2×2optical devices 372 arranged at log₂r consecutive stages. In the Banyannetwork, paths extend from all of the input ports to all of the outputports. FIG. 11 shows another specific configuration including planewaveguides 374 a and 374 b and channel waveguides 375 connecting themtogether. The channel waveguides 375 are provided with phase controlelectrodes 376. By controlling voltage to be applied to the phasecontrol electrodes 376, it is possible to send an input from a desiredinput port to a desired output port. FIG. 12 shows still anotherspecific configuration including a star coupler 378 and two groups ofoptical gates 377 a and 377 b respectively preceding and following thestar coupler 378. The optical gates 377 a and 377 b between a desiredinput port and a desired output port are opened to set up a channel viathe star coupler 378.

The device shown in FIG. 7 is also applicable to the 1×m opticalswitches 351 a shown in FIG. 9. Generally, among devices having n inputsand r outputs each, a device capable of controlling only a single pathis simpler in configuration than the other devices capable ofcontrolling two or more paths.

As for the number Ts of optical devices included in each of the matrixswitches 302 a-1 through 302 a-r, assume that the 1×m device 351 a has atree configuration of 1×2 optical devices, and that the n×r opticalswitch 361 has the Banyan configuration shown in FIG. 10. Then, thenumber Ts is expressed as:

Ts=n(m−1)+(mr/2)log₂ r

Assuming that the optical switch scale N is nr, and that m is 2n on thebasis of the non-blocking condition of m≧2n−1, then the number Ts isrewritten as:

Ts=(N/r) (2N/r−1)+Nlog₂ r

Assuming that N and r are 64 and 8, respectively, then the number Ts is8×(16−1)+64×3=312 and substantially equal to the number of opticaldevices included in a conventional 16×16 scale (N=16) optical matrixswitch. In this manner, the illustrative embodiment noticeably reducesthe number of optical devices and thereby scales down the individualoptical matrix switch.

In addition, the illustrative embodiment makes crosstalk negligible bypreventing two or more signals from being input to the 1×m opticalswitch 351 a or the n×r optical switch 361 at the same time.

Referring to FIGS. 13 and 14, another alternative embodiment of thepresent invention will be described which constitutes an improvementover the network 200 shown in FIG. 5. As shown, an optical switchcircuit network includes an optical matrix switch 402 a-1 arranged atits input side in place of the matrix switch 202 a-1 of FIG. 7. Ofcourse, optical matrix switches 402 a-2 through 402 a-r/h identical inconfiguration with the matrix switch 402 a-1 are substituted for thematrix switches 202 a-2 through 202 a-r/h of FIG. 5 although not shownspecifically. Likewise, the matrix switches 202 b-1 through 202 b-r/harranged at the output side each are configured symmetrically to thematrix switch 402 a-1 of FIG. 13 in the right-and-1eft direction.

As shown in FIG. 13, the matrix switch 402 a-1 has at its input siden/h′ groups of h h′×m/h′ optical switches 451 a-1 through 451 a-h. Thenh inputs are divided into groups of h′ inputs and connected to nh/h′h′×m/h′ optical switches in total. It is to be noted that h, h′, m and nare positive integers. The matrix switch 402 a-1 has at its output sidem/h′ nh/h′×h′r optical switches 430-1 through 430-(m/h′). The opticalswitches 430-1 through 430-(m/h′) each are made up of n/h′×h′ opticalswitches 451 b-1 through 451 b-h and h′ h×r optical switches 425 aarranged at the input side and output side, respectively. The opticalswitches 451 b and h×r optical switches 425 a are cross-connected toeach other.

The matrix switch 402 a-1 has n/h′ groups of h h′×m/h′ optical switches451 a-1 through 451 a-h, as stated above. The first h′×m/h′ opticalswitch 451 a-1 of each group is connected to the first n/h′×h′ opticalswitches 451 b-1 of the optical switches 430-1 through 430(m/h′) bytape-like optical fibers 803 each having h′ connect lines. Generally,the i-th (i being an integer between 1 and h, inclusive) h′×m/h′ opticalswitch 45 1 a-i of each group is connected to the i-th n/h′×h′ opticalswitches 451 b-i of the optical switches 430-1 through 430-(m/h′) bytape-like optical fibers each having h′ connect lines.

The configuration of each of the n/h′×h′r optical switches 430-1 through430-(m/h′) shown in FIG. 13 is only illustrative. As shown in FIG. 14,the crux is that each optical switch has any desired nh/h′×h′r opticalswitches.

The above network is successful to further reduce the number of opticaldevices of each matrix switch and therefore to further scale down theindividual matrix switch.

Still another alternative embodiment of the present invention will bedescribed with reference to FIG. 15. As shown, an optical switch circuitnetwork, generally 500, includes a first input section 520 a-1 havingN/2 (N being a natural number) first input ports and 1×2 opticalswitches 521 respectively connected to the first input ports. Likewise,a second input section 520 a-2 has N/2 second input ports and 1×2optical switches 521 respectively connected to the second input ports. Afirst output section 520 b-1 has N/2 first output ports and 2×1 opticalswitches 561 respectively connected to the first output ports. A secondoutput section 520 b-2 has N/2 second output ports and 2×1 opticalswitches 561 respectively connected to the second output ports. N/2×N/2optical matrix switches 502-1 through 502-4 each set up a particularoptical path between the first input ports or the second input ports andthe first output ports or the second output ports. The matrix switches502-1 through 502-4 may be provided with a crossbar configuration by wayof example.

More specifically, the 1×2 matrix switches 521 of the first inputsection 520 a-1 each are connected to the matrix switches 502-1 and502-2. Likewise, the 1×2 optical switches 521 of the second inputsection 520 a-2 each are connected to the matrix switches 502-3 and502-4. In the illustrative embodiment, the optical switches 521 each arecaused to select an adequate path by control means not shown.

In the illustrative embodiment, the optical switches 521 are implementedby TO switches by way of example. In this case, the above control meansselectively turns on or turns off drive heaters, not shown, so as tovary the resistances of waveguides and thereby switch the path for anoptical signal. This kind of control means using drive heaters will bedescribed specifically. In FIG. 15, the optical switches 521 are assumedto select paths 503 a indicated by thick lines when the control meansturns on a drive heater, but select paths 503 b indicated by thin lineswhen it turns off the drive heater. Also, assume that the opticalswitches 561 select paths 505 a indicated by thick lines in FIG. 15 whenthe control means turns on a drive heater, but select paths 505 bindicated by thin lines when it turns off the drive heater.

An optical signal input to any one of the input ports of the first inputsection 520 a-1 is sent to the matrix switch 502-1 if the drive heaterassigned to the optical switches 521 of the input section 520 a-1 is inits ON state. The optical signal is sent to the other matrix switch502-2 if the above drive heater is in its OFF state. Likewise, anoptical signal input to any one of the input ports of the second inputsection 520 a-2 is sent to the matrix switch 502-4 if the drive heaterassigned to the input section 520 a-2 is in its ON state, but sent tothe other matrix switch 502-3 if it is in its OFF state.

The 2×1 optical switches 561 of the first output section 520 b-1 areconnected to the matrix switches 502-1 and 502-3. The 2×1 opticalswitches 561 of the second output section 520 b-2 are connected to thematrix switches 502-2 and 502-4. An optical signal to be output from anyone of the output ports of the first output section 520 b-1 is outputfrom the matrix switch 502-3 if a drive heater assigned to the opticalswitches 561 of the output section 520 b-1 is in its ON state, butoutput from the matrix switch 502-1 if it is in its OFF state. Likewise,an optical signal to be output from any one of the output ports of thefirst output section 520 b-2 is output from the matrix switch 502-2 if adrive heater assigned the output section 502 b-2 is in its ON state, butoutput from the matrix switch 502-4 if it is in its OFF state.

In the above network 500, one of the drive heaters assigned to the inputsections 520 a-1 and 520 a-2 is turned on while the other heater isturned off, without regard to the path through which an optical signalis propagated. This is also true with the drive heaters assigned to theoutput sections 520 b-1 and 520 b-2. In addition, when the matrixswitches 502-1 through 502-4 are provided with a crossbar configuration,only one optical switch is turned on in each matrix switch. Therefore,assuming that the number of input ports and that of output ports are N,N drive heaters are turned on in the matrix switches and in either oneof the connection to the input side of the matrix switches and theconnection to the output side of the same, i.e., 2N drive heaters areturned on in total.

In a conventional optical switch circuit network, 3N drive heaters, inthe worst case, are turned on at the same time. The illustrativeembodiment therefore reduces drive power necessary for the TO switchesto ⅔. In addition, the illustrative embodiment is successful to maintainthe drive power constant without regard to the path along which anoptical signal is propagated.

Moreover, the matrix switches 502-1 through 502-4 with the crossbarconfiguration and the 1×2 optical switches 521 and 2×1 optical switches561 are combined in a tree structure. This configuration makes thedevices shorter than the conventional crossbar configuration and reducesthe drive power to 1/log₂N, compared to the configuration made up of Nstages of 1×2 optical switches and 2×1 optical switches.

Reference will be made to FIG. 16 for describing yet another alternativeembodiment of the present invention. This embodiment is an improvedversion of the embodiment of FIG. 15 and characterized in that eachmatrix switch for switching the optical paths is divided at its centerand has its two portions integrated with the input section and outputsection, respectively.

As shown in FIG. 16, an optical switch circuit network, generally 600,includes an input section 620 a-1 including N/2 input ports, N/2×N/2optical switches 622 a-1 and 622 a-2, and 1×2 optical switches 621connecting the input ports and optical switches 622 a-1 and 622 a-2.Likewise, an input section 620 a-2 including N/2 input ports, N/2×N/2optical switches 622 a-3 and 622 a-4, and 1×2 optical switches 621connecting the input ports and optical switches 622 a-3 and 622 a-4. Anoutput section 620 b-1 includes N/2 output ports, N/2×N/2 opticalswitches 622 b-1 and 622 b-2, and 1×2 optical switches connecting theoptical switches 622 b-1 and 622 b-2 and output ports. An output section620 b-2 includes N/2 output ports, N/2×N/2 optical switches 622 b-3 and622 b-4, and 1×2 optical switches connecting the optical switches 622b-3 and 622 b-4 and output ports.

The optical switch 622 a-1 of the input section 620 a-1 is connected tothe optical switch 622 b-1 of the output section 620 b-1. The opticalswitch 622 a-2 of the input section 620 a-1 is connected to the opticalswitch 622 b-3 of the output section 620 b-2. The optical switch 622 a-3of the input section 620 a-2 is connected to the optical switch 622 b-2of the output section 620 b-1. Further, the optical switch 622 a-4 ofthe input section 620 a-2 is connected to the optical switch 622 b-4 ofthe output section 620 b-2.

The network 600 is substantially identical with the previous network 500as to the connection between the 2×2 optical switches 621 and theoptical switches 622 a-1 through 622 a-4 and the connection between the2×1 optical switches 661 and the optical switches 622 b-1 through 622b-4. Consequently, whichever the path along which an optical signal ispropagated to an output port may be, it is necessarily propagated oncethrough a path on which a drive heater is in its ON state (thick line603 a or 605 b) and once through a path on which the drive heater is inits OFF state (thin line 603 b or 605 b).

The network 600 also achieves the advantages described in relation tothe network 500. In addition, the network 600 is advantageous in thateven when the number N of input ports and output ports is increased, thenetwork 600 can be easily integrated by dividing matrix switches withthe above principle.

FIG. 17 shows a further alternative embodiment of the present inventionwhich is a further improved version of the above network 600. As shown,an optical switch circuit network, generally 700, includes inputsections 720 a-1 through 720 a-4 and output sections 720 b-1 through 720b-4. The input sections 720 a-1 through 720 a-4 each include 1×2 opticalswitches 721 a and 721 b arranged at two consecutive stages in a treeconfiguration. Likewise, the output sections 720 b-1 through 720 b-4each include 2×1 optical switches 761 a and 761 b arranged at twoconsecutive stages in a tree configuration.

More specifically, the input section 720 a-1 has N/4 input ports andfour N/4×N/4 optical switches 722 a in addition to the 1×2 opticalswitches 721 a and 721 b connecting the input ports and optical switches722 a. The other input sections 720 a-2 through 720 a-4 have the sameconfiguration as the input section 720 a-1. The output section 720 b-1has N/4 output ports and four N/4×N/4 optical switches 722b in additionto the 2×1 optical switches 761 a and 761 b connecting the output portsand optical switches 722 b. The other output sections 720 b-2 through720 b-4 are identical in configuration with the output section 720 b-1.

In the i-th (i being an integer between 1 and 4, inclusive) inputsection 720 a-I, the j-th (j being an integer between 1 and 4,inclusive) optical switch 722 a is connected to the i-th optical switch722 b of the j-th output section 720-j. The N/4 input ports each areselectively connected to one of the four optical switches 722 a via the1×2 optical switches 721 a and 721 b arranged in a two-stage treeconfiguration. More specifically, the optical switches 721 a and 721 beach are driven by a respective drive heater. By selectively turning onand turning off such drive heaters, 2² different paths, i.e., fourdifferent paths are available for each input port.

The N/4 output ports each are selectively connected to one of the fouroptical switches 722 b via the 2×1 optical switches 761 a and 761 b alsoarranged in a two-stage tree configuration. More specifically, theoptical switches 761 a and 761 b each are driven by a respective driveheater. By selectively turning on and turning off such drive heaters, 2²different paths, i.e., four different paths are available for eachoutput port. The drive heaters of the input side and those of the outputside are symmetrical to each other with respect to the ON/OFF state. Forexample, assume that an optical signal is propagated through any path ofthe input side on which the drive heater assigned to the opticalswitches 721 a turns on (thick line) and any path on which the driveheater assigned to the optical switches 721 b turns off (thin line).Then, at the output side, the above signal is propagated through a pathon which the drive heater assigned to the optical switches 761 a turnson and a path on which the drive heater assigned to the optical switches761 b turns off.

The above network 700 is capable of using N/4×N/4 optical switches asthe optical switches 722 a and 722 b of the input side. Therefore, thenetwork scale N can be increased without sophisticating the connectionbetween the input ports and the optical switches 722 a or the connectionbetween the optical switches 722 b and the output ports. By arrangingthe optical switches in a symmetrical configuration, it is possible toreduce the total drive power of the entire network 700.

In the network 700, only the drive heaters of two of the opticalswitches 721 a, 721 b, 761 a and 761 b are turned on on the path of anoptical signal. Required drive power is N in the optical matrix switchand 2N on the path connected to the matrix switch (input or output),i.e., 3N in total.

Assume that the optical switches 721 a and 721 b or the optical switches761 a and 761 b are arranged in log₂(N/m) stages where m denotes thenumber of inputs of each matrix switch 722 a or the number of outputs ofeach matrix switch 722 b. Then, log₂(N/m)+1 optical switches are turnedon. It follows that drive power is reduced to(log₂(N/m)+1)/(2log₂(N/m)+1), compared to the case wherein considerationis not given to the drive states of the optical switches 721 a and 721 bor 761 a and 761 b.

As stated above, the illustrative embodiment successfully reduces thedevice length and minimizes an increase in drive power.

The configurations of the devices included in the above illustrativeembodiments are only illustrative. Any desired devices may be replacedwith each other so long as they are of the same scale. Further, in theembodiments shown in FIGS. 16 and 17, the 1×2 optical switches and 2×1optical switches each may be arranged in a grater number of stages inorder to obviate sophisticated connect paths and to facilitateintegration.

In summary, it will be seen that the present invention provides anoptical switch circuit network using only two stages of optical matrixswitches, scaling down the individual optical matrix switch, andreducing the number of devices. Further, the network of the inventionreduces the network length and drive power necessary for TO switcheswhile stabilizing the drive power, and obviates sophisticated connectionpaths ascribable to the extension of input ports and output ports whilepromoting easy integration.

The entire disclosure of Japanese patent application No. 35937/1999filed Feb. 15, 1999 including the specification, claims, accompanyingdrawings and abstract of the disclosure is incorporated herein byreference in its entirety.

While the present invention has been described with reference to theillustrative embodiments, it is not to be restricted by the embodiments.It is to be appreciated that those skilled in the art can change ormodify the embodiments without departing from the scope and spirit ofthe present invention.

What is claimed is:
 1. An optical switch circuit network including nrinput ports and nr output ports, n and r being positive integers,comprising: r/h input matrix switches, h being a positive integer,arranged at an input side of the optical switch circuit network and eachcomprising nh input ports of the nr input ports, m h×r optical switchesand h n×m optical switches each being connected to a group of n inputports of the nr input ports to thereby switch a path between the n inputports and said m h×r optical switches; and r/h output matrix switchesarranged at an output side of the optical switch circuit network andeach comprising nh output ports of the nr output ports, m r×h opticalswitches and h m×n optical switches each being connected to a group of noutput ports of the nr output ports to thereby switch a path between then output ports and said m r×h optical switches; wherein an i-th h×roptical switch, i being an integer between 1 and m, including 1 and m,of each of said r/h input matrix switches is connected to an i-th r×hoptical switch of each of said r/h output matrix switches by a tape-likeoptical fiber constituted by h connect lines, wherein h>1.
 2. An opticalswitch circuit network including nr, n and r being positive integers,input ports and nr output ports, comprising: r/h input matrix switchesarranged at an input side of the optical switch circuit network and eachcomprising nh input ports of the nr input ports, m/h′ nh/h′×h′r opticalswitches, where h and h′ are positive integers, and nh/h′ h′×m/h′optical switches each being connected to a group of h′ input ports ofthe nr input ports to thereby switch a path between the h′ input portsand said m/h′ nh/h′×h′r optical switches; and r/h output matrix switchesarranged at an output side of the optical switch circuit network andeach comprising nh output ports of the nr output ports, m/h′ h′r×nh/h′optical switches and nh/h′ m/h′×h′ optical switches each being connectedto a group of h′ output ports of the nr output ports to thereby switch apath between the h′ output ports and said m/h′ h′r×nh/h′ opticalswitches; each of said nh/h′ h′×m/h′ optical switches of each of saidr/h input matrix switches being connected to each of said m/h′ nh/h′×h′roptical switches of the r/h input matrix switch by tape-like opticalfibers each comprising h′ connect lines; each of said m/h′ h′r×nh/h′optical switches of each of said r/h output matrix switches beingconnected to said nh/h′ m/h′×h′ optical switches of the r/h outputmatrix switch by tape-like optical fibers each comprising h′ connectlines; each of said r/h input matrix switches being connected to each ofsaid r/h output matrix switches by tape-like optical fibers eachcomprising h connect lines, wherein h>1.
 3. A network in accordance withclaim 2, wherein said nh/h′ h′×m/h′ optical switches of each of said r/hinput matrix switches comprise n/h′ input optical switch groups, whereeach group comprises of h h′×m/h′ optical switches; each of said m/h′nh/h′×h′r optical switches of each of said r/h input matrix switchescomprises h n/h′×h′ optical switches and h′ h×r optical switches eachbeing connected to said h n/h′×h′ optical switches; said nh/h′ m/h′×h′optical switches of each of said r/h output matrix switches comprisen/h′ output optical switch groups, where each group comprises of hm/h′×h′ optical switches; each of said m/h′ h′r×nh/h′ optical switchesof each of said r/h output matrix switches comprises h h′×n/h′ opticalswitches and h′ r×h optical switches each being connected to said hh′×n/h′ optical switches; an i-th h′×m/h′ optical switch, i being aninteger between 1 and h, including 1 and h, in each of said n/h′ inputoptical switch groups of each of said r/h input matrix switches isconnected to an i-th n/h′×h′ optical switch of each of said m/h′nh/h′×h′r optical switches of the r/h input matrix switch by a tape-likeoptical fiber comprising h′ connect lines; an i-th m/h′×h′ opticalswitch of each of said n/h′ output optical switch groups of each of saidr/h output matrix switches is connected to an i-th h′×n/h′ opticalswitch of each of said m/h′ h′r×nh/h′ optical switches of the r/h outputmatrix switch by a tape-like optical fiber comprising h′ connect lines;and a j-th m/h′ nh/h′×h′r optical switch, j being an integer between 1and m/h′, including 1 and m/h′, of each of said r/h input matrixswitches is connected to a j-th m/h′ h′r×nh/h′ optical switch of each ofsaid r/h output matrix switches by a tape-like optical fiber comprisingh connect lines.
 4. An optical switch circuit network for receiving nrinput signals and outputting nr output signals, where n and r arepositive integers, comprising: r/h input matrix switches for eachreceiving nh of said nr input signals, each of said input matrixswitches having h nxm input optical switch stages and m hxr inputoptical switches, each of said input optical switches outputting rsignals, and wherein each of said input optical switch stages receives nof said input signals and outputs m signals to said m input opticalswitches; r/h output matrix switches for each outputting nh of said nroutput signals, each of said output matrix switches having m rxh outputoptical switches and h mxn output optical switch stages, each of saidoutput optical switches receiving r signals from said input opticalswitches, and wherein each of said output optical switch stages outputsn of said output signals and receives m signals from said m outputoptical switches; and a plurality of tape-like optical fibers, eachconstituted by h connect lines, connecting each of said input opticalswitches to a corresponding output optical switch, wherein h>1.
 5. Anoptical switch circuit network for receiving nr input signals andoutputting nr output signals, where n and r are positive integers,comprising: r/h input matrix switches for each receiving nh of the nrinput signals, each of said input matrix switches having nh/h′ h′×m/h′input optical switch stages, where h and h′ are positive integers, andm/h′ nh/h′×h′r input optical switches, wherein each of said inputoptical switch stages receives a group of h′ input signals and outputsm/h′ signals to said input optical switches; and r/h output matrixswitches for each outputting nh of the nr output signals, each of saidr/h output matrix switches having m/h′ h′r×nh/h′ optical switches andnh/h′ m/h′×h′ optical switch stages, each of said output optical switchstages outputs a group of h′ signals and receives m/h′ signals from saidoutput optical switches; each of said input optical switch stages ofeach of said r/h input matrix switches being connected to each of saidinput optical switches of the r/h input matrix switch by tape-likeoptical fibers each comprising h′ connect lines; each of said outputoptical switches of each of said r/h output matrix switches beingconnected to said output optical switch stages of the r/h output matrixswitch by tape-like optical fibers each comprising h′ connect lines;each of said r/h input matrix switches being connected to each of saidr/h output matrix switches by tape-like optical fibers each comprising hconnect lines, wherein h>1.
 6. A network in accordance with claimwherein said input optical switch stages of each of said r/h inputmatrix switches form n/h′ input optical switch groups, where each groupcomprises of h h′×m/h′ optical switches; each of said input opticalswitches of each of said r/h input matrix switches comprises h n/h′×h′optical switches and h′ h×r optical switches each being connected tosaid h n/h′×h′ optical switches; said output optical switch stages ofeach of said r/h output matrix switches form n/h′ output optical switchgroups, where each group comprises of h m/h′×h′ optical switches; eachof said output optical switches of each of said r/h output matrixswitches comprises h h′×n/h′ optical switches and h′ r×h opticalswitches each being connected to said h h′×n/h′ optical switches; eachh′×m/h′ optical switch in each of said n/h′ input optical switch groupsof each of said r/h input matrix switches is connected to acorresponding n/h′×h′ optical switch of each of said input opticalswitches of the r/h input matrix switch by a tape-like optical fibercomprising h′ connect lines; each m/h′×h′ optical switch of each of saidnih′ output optical switch groups of each of said r/h output matrixswitches is connected to a corresponding h′×n/h′ optical switch of eachof said output optical switches of the r/h output matrix switch by atape-like optical fiber comprising h′ connect lines; and each inputoptical switch of each of said r/h input matrix switches is connected toa corresponding output optical switch of each of said r/h output matrixswitches by a tape-like optical fiber comprising h connect lines.
 7. Anoptical switch circuit network including N input ports and N outputports, comprising: 2^(n) input sections each comprising N/2^(n) of saidN input ports, 2^(n)N/2^(n)×N/2^(n) input optical switches, and 2×1optical switches arranged in an n-stage tree configuration andconnecting said input ports and said input optical switches; and 2^(n)output sections each comprising N/2^(n) of said N output ports, 2^(n)N/2^(n)×N/2^(n) output optical switches, and 2×1 optical switchesarranged in an n-stage tree configuration and connecting said outputports and said output optical switches; a j-th (j being an integerbetween 1 and 2^(n), inclusive) input optical switch of an i-th (i beingan integer of 2^(n) or smaller) input section being connected to an i-thoutput optical switch of a j-th output section.
 8. A network inaccordance with claim 7, wherein the j-th input optical switch of thei-th input section and the i-th output optical switch of the j-th outputsection constitute an N/2^(n)×N/2^(n) optical switch.